Method of heating open-hearth furnace charges



Nov'.` 7, 1944. G. J. MORGAN 4 METHOD OF HEATING OPEN-HEARTH FURNACE CHARGES Filed April 13, 1942 INVENTOR G/VJ. MORGAN,

Patented Nov. 7, 1944 Y, o'EFicE METHOD OF HEATING OPEN-HEARTH FURNACE- CHARGES Guy/J, Morgan, Poland, hio

Application April 13, 1942, Serial No. 438,704

12 Claims.

This invention relates broadly to the manufacture of steel and, more particularly, to the heating .of the charge in an open-hearth furnace.

Various types of fuels have been employed heretofore for heating open-hearth furnace charges. While gaseous fuel has been used principally, other types such as pulverized coal, fuel oil and tar have been utilized (The Making, Shaping and Treating of Steel, th edition, Camp and Francis, page 383). Single-jet burners delivering a mixture of steam and atomized oil have been utilized heretofore for firing open-hearth furnaces with fuel oil. These burners produced diverging flames which effected melting ofthe scrap initially charged into the furnace at a relatively slow rate from the exterior only of the pile. Attempts were made to increase the rate at which scrap could be melted by increasing the velocity of the com bustible as delivered from the burner. rIhis expedient, however, produced a condition of slight vacuum at the firing end of the furnace and excess pressure at the stack end even though the pressure at the center of the roof was .05 to .07 of water. This caused an inrush of cold air through the charging door wickets and'any other openings at the firing end, pushing hot gases toward the back of the furnace. The resulting concentration of hot gases at the lback of the furnace overheated the brick work of the roof and the high pressure at the stack end also contributed to this result 4.by holding the hot gases against the roof.

In addition to the aforementioned objectionable conditions resulting from attempts to re openhearth furnaces with fuel oil, it has not been possible to change the character of the flame from the burner to suit it to the successive stages oi the steel-making operation because, with lthe sequent to the melting. In a preferred practice of theyinvention, I fire spaced, converging jets of a combustible such as a steam-oilmixture at relatively low velocity, and a central air jet at higher velocity adapted to produce an inductive effect upon the combustible jets, preventing substantial spreading of the ame whereby a sharp,

i. e., highly oxidizing llame results which is effective to oxidize and melt the scrap quickly. I also provide a simple and efficient burner capable of producing thorough atomization of steam and oil and adapted to deliver the converging combustible jets and the central air jet in such manner that the resulting flame impinges on a limited area of the surface of the scrap and thereby expedites the melting thereof. In addition to shortening the time required to melt the scrap, my invention produces more even distribution of the heat over the furnace roof, lthereby reducing the temperature thereof and the rate of deterioration.

Other advantages and novel features of the invention will be pointed out in greater detail during the following complete description and explanation which refer to the accompanying drawing. In the drawing,

Figure 1 is a partial longitudinal section through an open-hearth furnace showing the application of my burner thereto;

Figure 2 is a View partly in side elevation and partly in section along a central longitudinal plane showing the burner to enlarged scale;

Figure 3 is an end view with a part in section; and

Figure 4 is an elevation of a detail.

Referring in detail to the drawing and, for the present, to Figure 1, my novel burner indicated generally at Il) is mounted in the fuel port Il of an open-hearth furnace I2 having a bottom I3, roof I4', air inlet port I5 communicating with air uptakes I5a and charging doors I6. The burner may be supported inthe port Il by any suitable means (not shown) and has connections to suitalble sources of a combustible mixture such as steam and oil, and compressed air. As indicated 'in the drawing, the burner is positioned to deliver a sharp, concentrated flame I'I impinging on a relatively small area of the surface of a pile of scrap I8 built up on the bottom I3, and o n top of the limestone,` if any, forming part of the charge.

Before proceeding with a further explanation of the method of my invention the structure of the burner itself will be described in detail by reference to Figures 2 through 4, since the construction of the burner determines to a large extent the procedure contemplated by my invention. The burner per se is claimed in my application Serial No. 488,975 divided herefrom.

As best shown in Figure 2, the burner I 0 comprises a hollow cylindrical body 20. It may conveniently be formed from a length of pipe threaded at its ends to receive couplings 2l and 22. A

'oxidizing flame.

plug 23 is threaded into the coupling 2| and closes the forward end of the burner body. The plug 23 has a central air nozzle 24 and converging nozzles 25 spaced circumferentially thereof adapted to deliver jets of a combustible mixture such as steam and atomized oil. The inclination of the nozzles 25 is such that their axes intersect the axis of the nozzle 24 substantially at the point where the jets from the several nozzles impmge on the scrap piled in the furnace. The nozzles are of such length and diameter as to produce well defined, substantially linear jets of fluid when the latter is supplied thereto under suitable pressure.

Air is supplied to the nozzle 24 through an air tube 26 extending axially through the body 20 of the burner and having a nipple 2l welded to the extreme end thereof and threaded into the plug 23. The tube 26 extends through a plug 28 threaded into the coupling 22 and is connected to a suitable source of air under substantial pressure, e. g., 60-80# per square inch. The plug 28 is adapted to receive a packing gland 29 in its outer endl and is provided with studs 30 whereby the gland may be drawn home around the air tube 26.

A combustibile supply pipe 3| intersects the body tangentially and at an acute angle to the projection of the axis of the body whereby atomized steam and oil delivered through the pipe 3| to the body are caused to travel forward therealong while circling about interiorly thereof. This insures thorough agitation and completes the mixing of the steam and oil and the atomization of the latter. The initial mixing of the steam and oil and atomization of the latter may be effected by any suitable means such as a simple form of steam-jet injector.

Having described the structure of the burner, it remains to explain the method which I practice by the aid thereof.

When the scrap has been completely charged through the doors I6, I supply a combustible mixture such as steam and oil'through the pipe 3| and compressed air through tube 26 in such manner that on ignition, a sharp or oxidizing flame is projected from the burner onto the scrap pile, as indicated in the drawing at I l. The combustible mixture is preferably supplied under such pressure that combustion thereof will be substantially complete before striking the scrap pile. The air is delivered under sufficient pressure to impart to the jet discharged from the nozzle 24 a velocity somewhat greater than that ofthe jets of combustible, whereby the air stream by induction, draws the combustible radially inward of the flame, thereby preventing substantial spreading or diffusion and producing a sharp or As -a result, a highly oxidizing sting of flame follows along the central air stream which is effective to burn a hole in the pile of scrap. The method of adjusting the air and combustible supply will be explained later. 'I'he air supplied through the nozzle 24 affords the primary air for combustion of the fuel, at the same time secondary air is supplied through the air inlet port I5. Because of the sharp or oxidizing character of the flame and the central sting" or tongue in particular, the greater portion of the heat evolved by combustion is brought to bear 'on a relatively limited area of the surface of the scrap pile which is oxidized and the oxide melted in a relatively short time.

In addition to concentrating the flame, the air jet from the nozzle 24 (the -oxygen of which is eventually all consumed in the combustion of oil) also serves to remove the melted scrap progressively from the point where the flame impinges on the pile. As the scrap melts, the molten metal is blown aside by the air or oxidized, at least partially, and then blown away, exposing fresh surfaces of the piled scrap to the action of the burner flame. This progressive erosion of the surface of the pile quickly results in the formation of a hole in the pile into which the flame extends.

As the melting of the scrap proceeds in the manner indicated above, I increase the velocity of the air from nozzle 24 and combustible jets from the nozzles 25, thereby delivering a longer flame l adapted to enter the hole formed in the pile by the initial melting and erosion of the surface thereof. The fuel discharged into the hole eroded in the pile blows through the pile, traversing the crevices between the adjacent masses of metal therein, and burns by surface combustion. This heats the pile throughout from the interior thereof with the result that the melting, when once initiated, proceeds rapidly to completion with the accumulation of a bath of molten metal on the bottom I3.

After the Vscrap has been wholly melted, I modify the flame produced by my burner, to adapt it to the succeeding stage of the operation of the furnace. I reduce the pressure of the air supplied through tube 26 and increase the rate of fuel supply so that the burner delivers a soft, hot, luminous llame. Such flame is well adapted for the working of the charge after the addition of the molten pig iron. Under these conditions, the air entering the inlet I5 furnishes the greater portion of the oxygen needed for combustion. For the working of the charge, the valves controlling the air entering the inlet port |5 are adjusted to give 2% excess oxygen in the stack gases when the maximum amount of fuel needed for working the charge is being supplied to the burner I0, the waste gas sample being taken after i the scrap has been melted, the pig iron added and the bath is entirely covered by the slag. Even with the reduced velocity of the air jet, it is stillr effective to concentrate the burner ame on the bath, thereby tending to prevent overheating of the roof.

With the valves controlling the air entering the inlet I5 adjusted as just described, the desired melting flame will result if the pressure on the air supplied to nozzle 24 is raised to from 60 to #/sq. in. and the fuel reduced sufficiently to sharpen the flame or make it strongly oxidizing.

I may further modify the iiame after the charge has been fully worked, and convert it to a holding ame, if desired. I accomplish this by cutting ofi.' the air supply to the tube 26 and reducing the amount of the combustible delivered by the nozzles 25. The reducedamount of combustible is burned with the oxygen of the air entering the inlet port I5, producing a. yellow, highly reducing flame which is well suited for holding the charge at tapping heat. This holding flame will not burn the brick work.

In a particular instance, I have found that a good working flame may be obtained if the air supplied to the tube 26 is under a pressure of from 10 to 20#/sq. in. For the holding flame, the fuel should be reduced so that no unburned combustible passes out of the stack end of the furnace.

It will be apparent that my invention is characterized by numerous important advantages over prior methods o't heating open-hearth furnace charges and burners therefor. The principal advantage is the reduction inthe time re quired to melt the scrap. In a particular operation, including a large number of heavy charges,

the time requiredto melt the scrap by my inveni tion was less by more than an hour, on the aver age, than the time formerly required. This reduction in melting time has a direct relation to the output of 'steel per hour, the increase being actually 1.5 tons per hour in the example mentioned.'

A further advantage of the invention is that a more nearly balanced condition of the pressure of the atmosphere in the furnace is obtained. The use of a burner having a plurality of fuel jets spaced circumferentially of a central air jet permits the fuel velocity to be reduced materially, (for instance, in the ratio of 1:9 in the burner disclosed) as compared to the burners previously used having a single fuel nozzle. In other words, my burner produces a positive pressure on the furnace gases at both the firing end and the stack end but the pressure at the stack end is much less than that created by the use of the burners previously installed. Because of the fact that the gas pressure in the furnace is nearly balanced and is positive at all points, short flames blow out through the wicket holes in all charging doors and all other openings so that no cold air can enter to disturb the balanced condition. As a result, the roof is heated to a substantially uniform temperature throughout its entire area without the occurrence of localized hot spots which cause accelerated deterioration of the brick work. In an actual furnace operation, careful measurements showed a reduction of 100 F. in

the temperature of the furnace roof when practic ing my invention, as compared to the previous practice on the same furnace. y

The furnace roof is protected from excessive heating not only during the scrap-melting period but also during the Working period because of the fact that the working flame, like the scrapmelting flame, is concentrated and is directed onto the bath so that the greater portion of the heat is absorbed by the latter and only a relatively small portion by the roof. This condition has a further desirable result in that it hastens the progress of events in the shaping or working of the charge.

The ability to modify the character of the flame discharged by the burner, to suit the several stages of the entire operation such as scrap melting, working, and holding, is, of course, an important advantage, particularly since it does not disturb the general setting of the furnace nor involve adjustment of the main air valves controlling the iiow of in-going air through the regenerator checkers, the uptake and inlet port into the furnace. All that is necessary to vary the character of the flame is the proper adjustment of the amount of fuel and high-pressure air supplied to my burner. This may be accomplished by the aid of small valves which may be easily operated by hand.

The burner itself, furthermore, is effective, as pointedout` above, to produce thorough mixture of the steam and fuel and atomization of the primary and secondary air in the neighborhood of the nozzle end of the burner.

AlthoughvI have described and illustrated only a preferredpractice and embodiment of my invention, it will be understood-that changes in the procedure and construction disclosed herein may be made without departing from the spirit of the invention or the scope of the appended-claims.

I claim:

l. In a method of heating an open-hearth furnace charge, the steps including discharging toward a pile of scrap in the furnace, spaced jets of combustible converging substantially on said pile, at a velocity such that combustion is substantially complete on contact of the flame with the pile, supplying secondary air around said jets, and discharging a stream of compressed primary air centrally of said jets and at a velocity greater than that of said jets, thereby inducing the combustible in said jets radially inward to prevent substantial spreading of the flame and forming an oxidizing tongue concentrated on a limited area of the surface of the pile.

2. In a method of heating an open-hearth fur-` nace charge, the steps including discharging toward a pile of scrap in the furnace, spaced jets of combustible converging substantially on said pile, supplying secondary air around said jets, and delivering a stream of compressed primary air centrally of said jets and at a velocity greater than that of said jets, thereby inducing the combustible in said jets radially inward to prevent substantial spreading of the flame and forming an oxidizing tongue of 'flame concentrated on a limited area of the surface of the pile which hastens the melting of the scrap.

3. In a method of heating an openhearth furnace charge, the steps including discharging toward a pile` of scrap in the furnace, spaced jets of combustible, supplying secondary air around said jets, and delivering a stream of compressed primary air centrally of said jets and at a velocity latter (oil or tar) by the steam with which it is greater than that of said jets, thereby inducing the combustible in said jets radially inward to prevent substantial spreading of the flame and forming an oxidizing tongue of flame concentrated on a limited area of the surface of the pile which hastens the melting of the scrap.

4. In a method'of heating an open-hearth furnace charge, the steps including discharging toward a pile of scrap in the furnace, spaced jets of combustible, and delivering a stream of compressed air centrally of said jets and at a velocity greater than that of said jets, thereby inducing the combustible in said jets radially inward to prevent substantial spreading of 4the flame and forming an oxidizing tongue of flame concentrated on a limited area of the surface of the pile which hastens the melting of the scrap,

5. In a method of heating an open-hearth furnace charge, the steps including discharging to- .ward a pile of scrap in the furnace, spaced jets of combustible, and delivering a stream of compressed air centrally of said jets ai; a velocity suflicient to induce the combustible in said jets radially inward to prevent substantial spreading ofthe flame whereby it formsvanoxidizing tongue.

ward a pile of scrap in the furnace, spaced jets of combustible converging substantially on said pile, and delivering a stream of compressed air centrally of said jets at a -velocity suillcient to induce the combustible in said jets radially inward to prevent substantiakspreading of the flame whereby it forms an oxidizing tongue of flame concentrated on a limited area of the surface of the pile which blows aside the resulting oxidized and liquefied metal thereby exposing fresh surfaces of the scrap to the heat of said flame.

'7. In a method of heating an open-hearth furnace charge, the steps including discharging toward a pile of scrap in the furnace, spaced jets of combustible, at a velocity such that combustion is substantially complete on contact of the flame with the pile, and delivering a stream of compressed air centrally of said jets at a velocity sufficient to induce the combustible in said jets radially inward to prevent substantial spreading of the flame whereby it forms an oxidizing tongue of flame concentrated on a limited area of the surface of the pile which blows aside the resulting oxidized and liquefied metal thereby exposing fresh surface of the scrap to the heat of said flame.

8. In a method of heating an open-hearth furnace charge, the steps includingr discharging toward a pile of scrap in the furnace, spaced jets of combustible, supplying secondary air around said jets, and delivering a stream of compressed primary air centrally of said jets at a velocity sufllcient to induce the combustible in said jets radially inward to prevent substantial spreading of the flame whereby it forms an oxidizing tongue of flame concentrated on a limited area of the surface of the pile which blows aside the resulting oxidized and liquefied metal thereby exposing fresh surfaces of the scrap to the heat of said flame.

9. In a method of heating an open-hearth furnace charge, the steps including discharging toward a pile of scrap in the furnace, spaced jets of combustible converging substantially on said pile, and delivering a, stream of compressed primary air centrally of said jets, to induce the combustible thereof radially inward and prevent substantial spreading of the flame thereby effecting localized melting and the blowing of a hole into the pile, permitting heating thereof from the interior, then when the scrap is melted, adjusting the air supply to convert the flame into a soft luminous flame eective on the bath for working the charge during the addition of the other components thereof.

10. In a method of heating an open-hearth furnace charge, thesteps including discharging toward a pile of scrap in the furnace, spaced jets of combustible converging substantially on said pile, and delivering a stream of compressed primary air centrally of said jets, to induce the combustible thereof radially inward and prevent substantial spreading of the flame thereby effecting localized melting and the blowing of a hole into the pile, permitting heating thereof` from the interior, then when the scrap is melted, adjusting the air supply to convert the flame to a soft luminous flame effective on the bath for working the charge during the addition of the other components thereof and finally terminating the supply of primary air to convert the flame to a highly reducing holding flame toward the end of the heat.

11. In a' method of heating an open-hearth furnace charge, the steps including fusing and blowing a hole into a pile of scrap in the furnace by a sharp, oxidizing flame, discharging a jet of primary air centrally of said flame, adjusting the flame to heat the pile interiorly, then, when the scrap is melted, adjusting the air supply to convert the flame to a soft luminous flame effective on the bath for working the charge during the addition of other components.

12. In a method of heating an open-hearth furnace charge, the steps including fusing a small area on a pile of scrap in the furnace by a sharp, oxidizing flame, discharging a jet of compressed primary air centrally of said flame thereby blowing a hole into the pile, adjusting the llame to heat the pile interiorly, then, when the scrap is melted, adjusting the air supply to convert; the flame to a soft luminous flame effective on the bath for working thev charge during the addition of other components and finally converting the flame to a highly reducing flame effective on the bath for holding the charge toward the end of the heat.

GUY J .i MORGAN. 

